I've just bought my second iPhone, but unlike the first one this one won't turn on out of the box. I assumed that it was because the battery is completely flat so I've put it on charge using the plug accessary included. It's been on charge for about 40-45 minutes now and no improvement. No charging indicators have appeared on the screen in that time, nor will it turn on still. The back of the iPhone and the screen feels pretty warm so the power is getting to it. Should I just leave it and it will eventually turn on, or shall I return the phone to the shop due to the phone having a fault? Any advice appreciated.